Optical transceiver, optical communication system, and optical transceiver control method

Abstract

A wavelength-variable light transmission unit (60) outputs a light signal (LS1) in which a superposition signal (SP1) for giving a command to an other optical transceiver is superposed on a main signal (MS1). A wavelength-variable light reception unit (20) receives a light signal (LS2) from the other optical transceiver. A control unit (70) controls the wavelength-variable light transmission unit (60) and the wavelength-variable light reception unit (20). The wavelength-variable light transmission unit (60) superposes the superposition signal (SP1) on the main signal (MS1) by modulating the main signal (MS1) into a signal which has a waveform such that the amplitude transitions between two levels by amplitude shift modulation or by phase shift modulation, and controls the amplitude of the superposition signal (SP1) on the basis of a value which is obtained by multiplying the amplitude of the main signal (MS1) by a predetermined ratio.

Description

[Technical Field]

[0001] The present invention relates to an optical transceiver, an optical communication system, and a method for controlling an optical transceiver. [Background technology]

[0002] Optical communication systems that enable optical communication by connecting terrestrial base stations via optical cables are widely used. Each base station is equipped with optical transmission equipment equipped with one or more optical transceivers. When an optical transceiver is first used, it must be initialized.

[0003] A technology has been disclosed in which the transmission rate, data format, and transmission format are adjusted between optical transceivers before data communication begins (Patent Document 1). In this technology, test signals with the transmission rate and transmission format set between the optical transceivers are transmitted and received between the optical transceivers. The transmission rate is set by comparing the transmission rate used to transmit the test signal with the transmission rate of the received test signal. The transmission format is set corresponding to the transmission path state estimated in response to error detection in the test signal. After the transmission rate and transmission format are determined, the data format is determined by transmitting and receiving information related to the data format. After these are determined, communication between the optical transceivers begins.

[0004] A method for initiating bidirectional data packet communication between optical transceivers that are not yet communicating has also been proposed (Patent Document 2). In this method, prior to the bidirectional data packet communication, a connection packet containing identification information for each optical transceiver and transmitted at a speed lower than the transmission speed of the data packet is sent and received between the optical transceivers via an optical fiber transmission line. Then, based on the identification information in the connection packet received by each optical transceiver, one optical transceiver is designated as the master and the other as the slave. The master optical transceiver then notifies the slave optical transceiver of the transmission method set by this notification using a configuration packet. Bidirectional communication between the optical transceivers is then performed using the transmission method set by this notification.

[0005] Furthermore, a method for negotiating wavelengths used for communication between optical modules in a PON (Passive Optical Network) system consisting of an OLT (Optical Line Terminal) and an ONU (Optical Network Unit) has been proposed (Patent Document 3). In this method, an optical module (referred to as a first optical module) periodically transmits a wavelength idle signal of a selected first wavelength to a counterpart optical module (referred to as a second optical module). This wavelength idle signal indicates that the selected first wavelength is available for use, and the second optical module, upon receiving the wavelength idle signal, transmits a wavelength request message of a second wavelength corresponding to the first wavelength to the first optical module. Upon receiving the wavelength request message, the first optical module transmits a wavelength grant message to the second optical module to grant use of the selected wavelength. This determines the wavelengths used for transmitting and receiving optical signals between the two optical modules. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-229298 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-229299 [Patent Document 3] Special Publication No. 2017-539142 Summary of the Invention [Problem to be solved by the invention]

[0007] Optical transmission equipment generally includes multiple optical transceivers, and various settings are made, such as setting the channel (wavelength) used by each optical transceiver for transmission and reception (see, for example, Patent Document 3). For this reason, a function for transmitting and receiving commands such as setting information between two corresponding optical transceivers is sometimes required. It is conceivable to transmit a command signal to the destination optical transceiver by modulating a high-frequency main signal representing a data signal and superimposing the command signal on it. In this case, however, it is necessary to establish a method for superimposing the command signal while maintaining the quality of the main signal.

[0008] The present invention has been made in view of the above circumstances, and has an object to superimpose a command signal on a main signal and output the superimposed signal from an optical transceiver while maintaining the quality of the main signal. [Means for solving the problem]

[0009] An optical transceiver according to one embodiment of the present invention comprises an optical transmitter that superimposes an optical signal for issuing commands to another optical transceiver onto a first main signal, which is an optical signal that transmits communication data to the other optical transceiver, and outputs the superimposed first optical signal; an optical receiver that receives a second optical signal from the other optical transceiver; and a controller that controls the optical transmitter and the optical receiver. The optical transmitter superimposes the first superimposed signal, which is the optical signal superimposed on the first main signal, onto the first main signal by modulating the first main signal using amplitude shift keying or phase shift keying to a signal having a waveform whose amplitude transitions between two levels, and controls the amplitude of the first superimposed signal based on a value obtained by multiplying the amplitude of the first main signal by a predetermined ratio.

[0010] An optical communication system according to one aspect of the present invention comprises two opposing optical transmission devices each having a plurality of optical transceivers and a first optical multiplexer / demultiplexer that multiplexes and outputs optical signals output by the plurality of optical transceivers and demultiplexes received optical signals to the plurality of optical transceivers according to channels, and an optical cable connecting the two opposing optical transmission devices, wherein the optical transceiver in one optical transmission device transmits an optical signal for giving a command to another optical transceiver in the other optical transmission device, and transmits communication data to the other optical transceiver. The optical transceiver comprises an optical transmitting unit that superimposes a main signal, which is an optical signal to be transmitted, and outputs the superimposed signal; an optical receiving unit that receives an optical signal from the other optical transceiver; and a control unit that controls the optical transmitting unit and the optical receiving unit. The optical transmitting unit superimposes the superimposed signal, which is the optical signal to be superimposed on the main signal, on the main signal by modulating the main signal using amplitude shift keying or phase shift keying to a signal having a waveform whose amplitude transitions between two levels, and controls the amplitude of the superimposed signal based on a value obtained by multiplying the amplitude of the main signal by a predetermined ratio.

[0011] A control method for an optical transceiver according to one aspect of the present invention includes an optical transmitter that superimposes an optical signal for issuing commands to another optical transceiver onto a main signal, which is an optical signal that transmits communication data to the other optical transceiver, and outputs the superimposed optical signal; an optical receiver that receives the optical signal from the other optical transceiver; and a controller that controls the optical transmitter and the optical receiver. The method superimposes a superimposed signal, which is the optical signal superimposed on the main signal, on the main signal by modulating the main signal using amplitude shift keying or phase shift keying to a signal having a waveform whose amplitude transitions between two levels, and controls the amplitude of the superimposed signal based on a value obtained by multiplying the amplitude of the main signal by a predetermined ratio. [Effects of the Invention]

[0012] According to the present invention, it is possible to superimpose a command signal on a main signal and output the superimposed signal from an optical transceiver while maintaining the quality of the main signal. [Brief explanation of the drawings]

[0013] [Figure 1]FIG. 1 is a diagram illustrating a basic configuration of an optical communication system according to a first embodiment. [Figure 2] 1 is a diagram illustrating a configuration of an optical transmission device according to a first embodiment and an example of transmission and reception of an optical signal; [Figure 3] FIG. 2 is a diagram illustrating a configuration of a channel setting optical signal. [Figure 4] FIG. 1 is a diagram illustrating a basic configuration of an optical transceiver according to a first embodiment. [Figure 5] FIG. 2 is a diagram illustrating a more detailed configuration of the optical transceiver according to the first embodiment. [Figure 6] FIG. 2 illustrates transmission of a channel setting optical signal in the optical transceiver according to the first embodiment. [Figure 7] FIG. 2 illustrates reception of a channel setting optical signal in the optical transceiver according to the first embodiment. [Figure 8] 10A and 10B are diagrams illustrating an example of a channel setting optical signal transmitted and received between two optical transceivers in a channel setting process. [Figure 9] FIG. 10 is a diagram showing state transitions in a channel setting process. [Figure 10] FIG. 10 is a diagram illustrating a configuration of an optical transceiver according to a second embodiment. [Figure 11] 10 is a diagram illustrating an example of a channel setting optical signal transmitted and received between two optical transceivers in a channel setting process according to the second embodiment. FIG. [Figure 12] FIG. 10 is a diagram illustrating a configuration of an optical transceiver according to a third embodiment. [Figure 13] FIG. 10 is a diagram illustrating a configuration of an optical communication system according to a third embodiment and an example of transmission and reception of an optical signal. [Figure 14] FIG. 11 is a diagram schematically illustrating a signal flow when controlling an optical transceiver of a communication partner in the third embodiment. [Figure 15] FIG. 11 is a diagram illustrating a signal flow when controlling a host device to which a communication partner optical transceiver is connected in the third embodiment. [Figure 16]FIG. 10 is a diagram illustrating a configuration of an optical transceiver according to a fourth embodiment. [Figure 17] FIG. 10 is a diagram illustrating a configuration of a wavelength-tunable optical transmitter according to a fourth embodiment. [Figure 18] 3A and 3B are diagrams schematically showing the waveform and eye pattern of a main signal before and after modulation. [Figure 19] FIG. 10 is a diagram illustrating a comparative example in which a main signal is modulated and a superimposed signal is superimposed. [Figure 20] 10A and 10B are diagrams illustrating changes in the amplitude of a superimposed signal in a comparative example when the amplification factor increases due to fluctuations in the characteristics of an optical transceiver. [Figure 21] 10A and 10B are diagrams illustrating changes in the amplitude of a superimposed signal in a comparative example when the gain is reduced due to fluctuations in the characteristics of the optical transceiver. [Figure 22] 10 is a diagram showing signal waveforms when the amplitude of a superimposed signal SP1 is controlled in accordance with the amplitude of an amplified main signal MS1 in the transceiver according to the first embodiment. FIG. [Figure 23] FIG. 10 is a diagram illustrating a configuration of an optical transceiver according to a fifth embodiment. [Figure 24] FIG. 1 is a diagram showing the relationship between signals and bits in Manchester encoding. [Figure 25] 10A and 10B are diagrams illustrating examples of optical signals transmitted by a transmitting optical transceiver. [Figure 26] FIG. 10 is a diagram illustrating an example of a superimposed signal for bit synchronization. [Figure 27] 13 is a flowchart showing the procedure of a bit synchronization operation in the seventh embodiment. [Figure 28] FIG. 10 is a diagram illustrating a first example of a bit synchronization operation. [Figure 29] FIG. 10 is a diagram illustrating a second example of a bit synchronization operation. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same elements are designated by the same reference numerals, and redundant explanations will be omitted as necessary.

[0015] Embodiment 1 An optical communication system 1000 according to a first embodiment will be described. FIG. 1 schematically illustrates a basic configuration of the optical communication system 1000 according to the first embodiment. In the optical communication system 1000, optical transmission devices 1 and 2 are provided in land terminal stations BS1 and BS2, respectively. The optical transmission devices 1 and 2 are connected by optical cables C1 and C2. The optical cables C1 and C2 may be laid on land or under the sea. In this example, the optical cable C1 is used as a cable for transmitting an optical signal transmitted from the optical transmission device 1 to the optical transmission device 2. The optical cable C2 is used as a cable for transmitting an optical signal transmitted from the optical transmission device 2 to the optical transmission device 1. Note that one or more optical amplifiers AMP may be inserted into the optical cables C1 and C2 to compensate for optical signals attenuated during transmission.

[0016] 1 shows a simplified configuration of the optical communication system for the sake of simplicity, and for example, one optical transmission device may be communicably connected to two or more optical transmission devices via an optical cable. Furthermore, an optical add / drop device that adds / drops optical signals may be inserted into the optical cable as needed to branch off branch paths from the trunk path. However, this is merely an example, and it goes without saying that the optical communication system may be configured to have any path (trunk path and branch path) that enables optical communication between any number of optical transmission devices.

[0017] The configuration of an optical transmission device will be explained below. The optical transmission device has multiple optical transceivers, an optical multiplexer that multiplexes optical signals to be transmitted and outputs a multiplexed optical signal, and an optical demultiplexer that demultiplexes the received multiplexed optical signal to each optical transceiver. For simplicity, the optical multiplexer and optical demultiplexer will be combined and treated as a single optical multiplexer / demultiplexer below.

[0018] 2 schematically illustrates an example of the configuration of optical transmission devices 1 and 2 according to the first embodiment and the transmission and reception of optical signals. The optical transmission device 1 includes a plurality of optical transceivers and an optical multiplexer / demultiplexer M1 (also referred to as a second optical multiplexer / demultiplexer). In this example, the optical transmission device 1 includes 25 optical transceivers A1 to A25. Two different channels are assigned to each of the optical transceivers A1 to A25.

[0019] The number of ports of the optical multiplexer / demultiplexer M1 connected to the optical transceivers is equal to the number of channels. The transmit port of optical transceiver Ai (i is an integer between 1 and 25) is connected to the port for channel CH(2i-1) of the optical multiplexer / demultiplexer M1, and the receive port is connected to the port for channel CH(2i). In other words, the optical transceiver Ai is assigned the transmit channel CH(2i-1) and the receive channel CH(2i). That is, the optical transceivers A1, A2, A3, ..., A25 are assigned the channels CH1 and CH2, CH3 and CH4, CH5 and CH6, ..., CH49 and CH50. In this way, a specific channel is assigned to each of the two ports of the optical transceiver, with no overlap within the optical transmission device.

[0020] The optical transmission device 2 has the same configuration as the optical transmission device 1. That is, the optical transmission device 2 has 25 optical transceivers B1 to B25 and an optical multiplexer / demultiplexer M2 (also referred to as a first optical multiplexer / demultiplexer).

[0021] The number of ports of the optical multiplexer / demultiplexer M2 connected to the optical transceivers is equal to the number of channels. The receiving port of the optical transceiver Bi is connected to the port for channel CH(2i-1) of the optical multiplexer / demultiplexer M2, and the transmitting port is connected to the port for channel CH(2i). In other words, the optical transceiver Bi is assigned a transmitting channel CH(2i) and a receiving channel CH(2i-1). That is, the optical transceivers B1, B2, B3, ..., B25 are assigned channels CH1 and CH2, CH3 and CH4, CH5 and CH6, ..., CH49 and CH50. In this way, a specific channel is assigned to each of the two ports of the optical transceiver, with no overlap within the optical transmission device.

[0022] With the above configuration, two common channels are assigned to the optical transceiver Ai and the optical transceiver Bi, and optical signals can be transmitted and received using these two channels.

[0023] This example shows the transmission and reception paths of optical signals, focusing on optical transceiver A2 in optical transmission device 1 and optical transceiver B2 in optical transmission device 2. Optical transceiver A2 transmits an optical signal using channel CH3, and the transmitted optical signal on channel CH3 is received by optical transceiver B2. Optical transceiver B2 also transmits an optical signal using channel CH4, and the transmitted optical signal on channel CH4 is received by optical transceiver A2.

[0024] In FIG. 2, for the sake of simplicity, attention is focused on optical transceiver A2 and optical transceiver B2, and it goes without saying that other optical transceivers can also transmit and receive optical signals using two channels in the same manner.

[0025] In this way, to transmit and receive optical signals on a specific channel, the channel to be used must be set in the optical transceiver on the transmitting side and the optical transceiver on the receiving side. Generally, the channel setting in the optical transceiver is performed as part of the initial setup procedure when the optical transceiver is installed in the optical transmission device.

[0026] However, for example, in the case of the optical communication system described above, which uses a maximum of 50 channels, two optical transmission devices require a total of 50 optical transceivers, each with two channels, for a total of 100 configuration operations. However, performing this configuration manually poses a problem in that it requires an enormous amount of time. Furthermore, since multiple configuration operations must be performed without error, manual configuration operations can be considered problematic from the standpoint of reliability.

[0027] In this embodiment, in order to address this problem, an optical transceiver that autonomously performs channel setting processing when attached to an optical transmission device will be described.

[0028] For example, when optical transceivers A2 and B2 are installed in an optical transmission device, the optical transceivers A2 and B2 autonomously execute channel setup processing, transmitting and receiving channel setup optical signals between the optical transceivers A2 and B2.

[0029] FIG. 3 shows a schematic diagram of the configuration of a channel setting optical signal. The channel setting optical signal S includes at least local channel information L and remote channel information R stored in the optical transceiver. The local channel information L indicates the channel of the channel setting optical signal S transmitted by the optical transceiver when the optical transceiver transmits the channel setting optical signal S during the channel setting process. The remote channel information R indicates the channel of the channel setting optical signal S received by the optical transceiver when the optical transceiver receives the channel setting optical signal S during the channel setting process. The channel setting optical signal S may include other information as necessary. FIG. 3 shows an example in which the channel setting optical signal S includes header information OH.

[0030] In this embodiment, the channel setting optical signal is superimposed on a main signal modulated based on a data signal to be transmitted and received between two optical transceivers (e.g., the above-mentioned optical transceivers A2 and B2) that transmit and receive optical signals, and then transmitted. The channel setting optical signal can be superimposed on the main signal and transmitted using a modulation method such as amplitude-shift keying (ASK), phase-shift keying (PSK), or frequency-shift keying (FSK). Note that the modulation methods shown here are merely examples, and various modulation methods can be applied as long as the channel setting optical signal can be superimposed on the main signal.

[0031] The configuration of the optical transceiver according to the present embodiment will now be described. Fig. 4 schematically shows the basic configuration of the optical transceiver according to the first embodiment. Fig. 5 shows the configuration of the optical transceiver according to the first embodiment in more detail. Note that since the optical transceivers A1 to A25 and B1 to B25 have similar configurations, the optical transceiver 100, which has the same structure as these transceivers, will be described as a representative example.

[0032] The optical transceiver 100 includes a tunable optical transmitter 10, a tunable optical receiver 20, and a controller 30. The controller 30 controls the operation of the tunable optical transmitter 10 and the tunable optical receiver 20 in response to, for example, a command signal INS provided from an optical transmission device in which the optical transceiver 100 is implemented. The controller 30 includes a processor 31 and a memory 32.

[0033] The wavelength-tunable optical transmitter 10 is configured to be able to change the wavelength of the optical signal to be transmitted, i.e., the channel. The wavelength-tunable optical transmitter 10 includes a driver 11 and an optical signal transmitter 12. The driver 11 outputs a drive signal DRV to the optical signal transmitter 12 based on a received main signal (data signal) IN. The wavelength-tunable optical signal transmitter 12 is configured, for example, as a Transmitter Optical Sub-Assembly (TOSA) and is configured to be able to output an optical signal LS1 modulated in accordance with the drive signal DRV. As described above, the optical transceiver 100 can output a main signal by superimposing a channel setting optical signal S1 on it. Therefore, the optical signal LS1 modulated in accordance with the drive signal DRV is an optical signal consisting of only the main signal MS1, or an optical signal in which the channel setting optical signal S1 is superimposed on the main signal MS1.

[0034] The wavelength-tunable optical receiving unit 20 is configured to be able to change the wavelength of the received optical signal, i.e., the channel. The wavelength-tunable optical receiving unit 20 includes an amplifier 21 and an optical signal receiving unit 22. The wavelength-tunable optical signal receiving unit 22 is configured, for example, as a receiver optical sub-assembly (ROSA). It converts the received optical signal LS2 into an electrical output signal DAT and outputs it to the amplifier 21. The amplifier 21 is configured, for example, as a limiting amplifier. It amplifies the output signal DAT to a predetermined amplitude and outputs the amplified output signal OUT to an external device outside the optical transceiver 100, such as an optical transmission device in which the optical transceiver 100 is implemented. As described above, the optical transceiver 100 can receive an optical signal in which a channel setting optical signal is superimposed on a main signal. Therefore, the optical signal LS2 can be an optical signal consisting of only the main signal MS2 or a signal in which the channel setting optical signal S2 is superimposed on the main signal MS2. When an optical signal in which a channel setting optical signal S is superimposed on a main signal MS is received, the amplifier unit 21 separates and outputs an output signal OUT based on the main signal MS from the output signal DAT, and separates and outputs a detection signal DET based on the channel setting optical signal S2 to the calculation unit 31 of the control unit 30.

[0035] Next, transmission of a channel setting optical signal in the optical transceiver 100 will be described. FIG. 6 illustrates transmission of the channel setting optical signal SA in the optical transceiver 100. Since FIG. 6 focuses on the channel setting optical signal S1, the main signal MS1 is not shown. The calculation unit 31 of the control unit 30 provides a control signal CON to the drive unit 11 to superimpose a channel setting signal on the drive signal DRV output by the drive unit 11. By including local channel information L and remote channel information R in the control signal CON, the channel setting optical signal S1 superimposed on the main signal MS1 output by the optical signal transmitter 12 includes the local channel information L and remote channel information R. The calculation unit 31 can read the local channel information L and remote channel information R to be included in the channel setting signal S1 from the storage unit 32 as needed. FIG. 6 shows an example of the channel setting optical signal S1, and it goes without saying that the signal S1 can be modulated appropriately in accordance with the modulation method for superimposing it on the main signal MS1.

[0036] Next, the reception of a channel setting optical signal in the optical transceiver 100 will be described. FIG. 7 illustrates the reception of the channel setting optical signal SB in the optical transceiver 100. Since FIG. 7 focuses on the channel setting optical signal S2, the main signal MS2 is not shown. When the optical signal receiver 22 receives an optical signal on which the channel setting optical signal S2 is superimposed, the amplifier 21 outputs a detection signal DET based on the channel setting optical signal S2 to the processor 31 of the controller 30. This allows the controller 30 to receive local channel information L and remote channel information R. The processor 31 can write the received local channel information L and remote channel information R to the memory 32 as appropriate. FIG. 7 illustrates an example of the channel setting optical signal S2, and it goes without saying that the channel setting optical signal S2 can be modulated as appropriate depending on the modulation method used to superimpose it on the main signal MS2.

[0037] Next, we will explain the channel setting process of the optical transceivers using the above-mentioned channel setting optical signals. Optical transceivers A2 and B2 change the local channel information L, i.e., by transmitting channel setting optical signals while sweeping the local channels, to determine the channels to be used for transmitting and receiving optical signals between them, following the procedure shown below. Figure 8 shows an example of the channel setting optical signals transmitted and received between optical transceivers A2 and B2 during the channel setting process. Figure 9 shows the state transitions during the channel setting process.

[0038] At the start of the channel setting process, the optical transceivers A2 and B2 are in an unknown state (hereinafter referred to as state EU: Each channel Unknown) in which the transmit and receive channels to be set are unknown. In other words, neither the optical transceiver that will be the transmission partner nor the optical transceiver that will transmit the received optical signal have been identified.

[0039] Thereafter, the optical transceivers A2 and B2 repeatedly transmit the channel setting optical signals while sweeping the local channels, starting from channel CH1 and proceeding in ascending order.

[0040] In the following, the optical transceiver B2 will also be referred to as the first optical transceiver, and the optical transceiver A2 will also be referred to as the second optical transceiver. The channel setting optical signal output by the optical transceiver B2 will also be referred to as the first channel setting optical signal. The channel setting optical signal output by the optical transceiver A2 will also be referred to as the second channel setting optical signal.

[0041] Channel CH3 is also referred to as the first channel, and channel CH4 is also referred to as the second channel.

[0042] The local channel information LB of the optical transceiver B2 is also referred to as the first channel information, and the local channel information LA of the optical transceiver A2 is also referred to as the second channel information. The remote channel information RB of the optical transceiver B2 is also referred to as the third channel information, and the local channel information LA of the optical transceiver A2 is also referred to as the second channel information.

[0043] (1) SA1 / LA:CH1, RA:NONE In the example of Figure 8, optical transceiver A2 first transmits a channel setting optical signal SA1 for channel CH1, with local channel information LA set to channel CH1 and remote channel information RA set to null (NONE). In this example, channel CH1 is the channel used for transmission from optical transceiver A1 to optical transceiver B1. That is, the port for channel CH1 of optical multiplexer / demultiplexer M2 of optical transmission device 2 is connected to the receiving port of optical transceiver B1. Therefore, the channel setting optical signal SA1 is blocked by optical multiplexer / demultiplexer M2 and does not reach optical transceiver B2.

[0044] (2)SB1 / LB:CH1,RB:NONE Next, optical transceiver B2 transmits a channel setting optical signal SB1 for channel CH1, with local channel information LB set to channel CH1 and remote channel information RB set to null (NONE). Because the transmit port of optical transceiver A1 is connected to the port for channel CH1 of optical multiplexer / demultiplexer M1 in optical transmission device 1, the channel setting optical signal SB1 is blocked by optical multiplexer / demultiplexer M1 and does not reach optical transceiver A2.

[0045] (3) SA2 / LA:CH2, RA:NONE Next, optical transceiver A2 transmits a channel setting optical signal SA2 for channel CH2, with local channel information LA set to channel CH2 and remote channel information RA set to null (NONE). In this example, channel CH2 is the channel used for transmission from optical transceiver B1 to optical transceiver A1. That is, the port for channel CH2 of optical multiplexer / demultiplexer M2 of optical transmission device 2 is connected to the transmit port of optical transceiver B1. Therefore, the channel setting optical signal SA2 is blocked by optical multiplexer / demultiplexer M2 and does not reach optical transceiver B2.

[0046] (4) SB2 / LA:CH2,RA:NONE Next, optical transceiver B2 transmits a channel setting optical signal SB2 for channel CH2, with local channel information LB set to channel CH2 and remote channel information RB set to null (NONE). Because the receiving port of optical transceiver A1 is connected to the port for channel CH2 of optical multiplexer / demultiplexer M1 in optical transmission device 1, the channel setting optical signal SB2 is blocked by optical multiplexer / demultiplexer M1 and does not reach optical transceiver A2.

[0047] (5)SA3 / LA:CH3,RA:NONE, state transition: EU→PK Next, the optical transceiver A2 transmits a channel setting optical signal SA3 for channel CH3, with local channel information L set to channel CH3 and remote channel information R set to null (NONE). In this example, channel CH3 is the channel used for transmission from the optical transceiver A2 to the optical transceiver B2. That is, the port for channel CH3 of the optical multiplexer / demultiplexer M2 of the optical transmission device 2 is connected to the receiving port of the optical transceiver B2. Therefore, the channel setting optical signal SA3 for channel CH3 is received by the optical transceiver B2 via the optical multiplexer / demultiplexer M2.

[0048] This allows the optical transceiver B2 to receive channel CH3 as the local channel information LA of the optical transceiver A2. Since the local channel information LA of the optical transceiver A2 is remote channel information RB for the optical transceiver B2, the optical transceiver B2 fixes the remote channel information RB to channel CH3.

[0049] At this time, the optical transceiver B2 enters a state in which it has detected the transmission channel of the partner optical transceiver A2 (state PK: Partner CH Known), and the state transitions from EU to PK.

[0050] (6)SB4 / LB:CH3,RB:NONE Next, optical transceiver B2 transmits a channel setting optical signal SB3 for channel CH3, whose local channel information LB is for channel CH3 and whose remote channel information RB is for channel CH3. Because the transmit port of optical transceiver A2 is connected to the port for channel CH3 of optical multiplexer / demultiplexer M1 in optical transmission device 1, the channel setting optical signal SB3 for channel CH3 is blocked by optical multiplexer / demultiplexer M1 and does not reach optical transceiver A2.

[0051] (7) SA4 / LA:CH4, RA:NONE Next, optical transceiver A2 transmits a channel setting optical signal SA4 for channel CH4, with local channel information LA set to channel CH4 and remote channel information RA set to null (NONE). In this example, channel CH4 is the channel used for transmission from optical transceiver B2 to optical transceiver A2. That is, the port for channel CH4 of optical multiplexer / demultiplexer M2 of optical transmission device 2 is connected to the transmit port of optical transceiver B2. Therefore, the channel setting optical signal SA4 for channel CH4 is blocked by optical multiplexer / demultiplexer M2 and does not reach optical transceiver B2.

[0052] (8) SB4 / LB: CH4, RA: CH3, state transition: EU → EK Next, optical transceiver B2 transmits a channel setting optical signal SB4 for channel CH4, with local channel information LB set to channel CH4 and remote channel information RB set to channel CH3. The receiving port of optical transceiver B2 is connected to the port for channel CH4 of optical multiplexer / demultiplexer M1 of optical transmission device 1. Therefore, the channel setting optical signal SB4 for channel CH4 is received by optical transceiver A2 via optical multiplexer / demultiplexer M1.

[0053] This allows the optical transceiver A2 to receive channel CH4 as the local channel information LB of the optical transceiver B2. Since the local channel information LB of the optical transceiver B2 is the remote channel information RA for the optical transceiver A2, the optical transceiver A2 fixes the remote channel information RA to channel CH4.

[0054] Furthermore, the optical transceiver A2 can receive channel CH3 as the remote channel information RB of the optical transceiver B2. Since the remote channel information RB of the optical transceiver B2 is local channel information LA for the optical transceiver A2, the optical transceiver A2 fixes the local channel information LA to channel CH3. Note that fixing the local channel information LA to channel CH3 sets the transmission channel for the optical transceiver A2, so the optical transceiver A2 stops channel sweeping.

[0055] At this time, the optical transceiver A2 enters a state where it has detected the transmission channel of the partner optical transceiver B2 and the channel available for transmission from the optical transceiver A2 to the optical transceiver B2 (state EK: Each CH Known), and the state transitions from EU to EK.

[0056] (9) SA0 / LA:CH3, RA:CH4, state transition:PK→EK Next, the optical transceiver A2 transmits a channel setting optical signal SA0 for channel CH3, in which the local channel information LA is fixed to channel CH3 and the remote channel information RA is fixed to channel CH4. The channel setting optical signal SA0 for channel CH3 is received by the optical transceiver B2.

[0057] In this case, the optical transceiver B2 can receive channel CH4 as the remote channel information RA of the optical transceiver A2. Since the remote channel information RA of the optical transceiver A2 is local channel information LB for the optical transceiver B2, the optical transceiver B2 fixes the local channel information LB to channel CH4. Note that fixing the local channel information LB to channel CH4 sets the transmission channel for the optical transceiver B2, so the optical transceiver B2 stops channel sweeping.

[0058] At this time, the optical transceiver B2 enters a state (state EK) in which it has detected the transmission channel of the partner optical transceiver A2 and a channel that can be transmitted from the optical transceiver B2 to the optical transceiver A2, and the state transitions from PK to EK.

[0059] (10)SB0 / LB:CH4,RB:CH3, State transition:EK→LE Next, the optical transceiver B2 transmits a channel setting optical signal SB0 for channel CH4, with the local channel information LB fixed to channel CH4 and the remote channel information RB fixed to channel CH3. The channel setting optical signal SB0 for channel CH4 is received by the optical transceiver A2.

[0060] In this case, the optical transceivers A2 and B2 can confirm that the local channel information LA of the optical transceiver A2 and the remote channel information RB of the optical transceiver B2 match channel CH3, and that the local channel information LB of the optical transceiver B2 and the remote channel information RA of the optical transceiver A2 match channel CH4. Therefore, in this case, the optical transceivers A2 and B2 can confirm that the channels to be used for transmission and reception have been determined. Therefore, since no further channel setting processing is required, the optical transceivers A2 and B2 conclude that the connection is established (state LE: Link Established) and end the channel setting processing.

[0061] As a result, after the channel setting process is completed, the optical transceiver A2 and the optical transceiver B2 can transmit and receive optical signals using the channels CH3 and CH4.

[0062] As described above, according to this configuration, the optical transceiver can autonomously set the channel of the optical signal to be transmitted and the channel of the optical signal to be received by referring to the information contained in the channel setting signal that it receives.

[0063] This makes it possible to reduce the time required to set channels in the optical transceiver, even when many channels are used, such as in the optical communication system described above.

[0064] In manual channel configuration, it may take minutes, for example, about 10 minutes, to configure one channel. In contrast, with this configuration, although this may vary depending on the configuration of the optical communication system, automatic configuration of one channel is possible in seconds, for example, in a few seconds. As such, it can be seen that this configuration significantly reduces the time required to configure channels in an optical transceiver.

[0065] Furthermore, by having the optical transceiver autonomously perform channel setting, not only can manual work by the worker be reduced, but the worker can also perform other tasks while the channel setting process is in progress, which is advantageous in terms of labor savings.

[0066] Furthermore, since the optical transceiver can autonomously perform channel setting, it is possible to prevent mistakes such as setting the wrong channel, which can occur when channel setting is done manually, and it is also possible to improve the reliability of channel setting.

[0067] It is possible that an optical transmission device may be initially operated with fewer optical transceivers than the maximum number of optical transceivers installed, and then additional optical transceivers may be added. Manual channel configuration in this case requires cumbersome tasks, such as checking which channels are already in use and then configuring channels other than those already in use. In contrast, the optical transceiver according to the present embodiment can autonomously configure channels even if the channels already in use are unknown, thereby reducing the time and labor required for adding additional optical transceivers.

[0068] Although the above description focuses on the optical transceivers A2 and B2, it goes without saying that the channel setting process can be similarly performed for the other optical transceivers A1, A3 to A25, B1, and B3 to B25.

[0069] Although the above description has been given of the case where the optical transceiver changes the channel of the channel setting optical signal in ascending order starting from channel CH1, this is merely an example. For example, the optical transceiver may change the channel of the channel setting optical signal in descending order. Furthermore, for example, the optical transceiver may change the channel of the channel setting optical signal in any order other than descending or ascending order.

[0070] Embodiment 2 In the first embodiment, an optical transceiver that autonomously performs channel setting has been described. However, if the channel to be used by the optical transceiver is known in advance, manual channel setting may improve the efficiency of the work. The optical transceiver according to the first embodiment sweeps channels when performing channel setting, but it is possible that a large number of channels may be swept before reaching the channel to be set. In this case, it takes a long time to complete channel setting. In contrast, if the channel to be used by the optical transceiver is known, manual channel setting can be performed even after autonomous channel setting has started, thereby eliminating the need for channel sweeping. This is expected to reduce the time required for channel setting and improve the efficiency of the channel setting work.

[0071] Therefore, in this embodiment, an optical transceiver capable of manual channel setting as well as autonomous channel setting will be described. Fig. 10 schematically illustrates the configuration of an optical transceiver 200 according to a second embodiment. The optical transceiver 200 has a configuration in which the control unit 30 of the optical transceiver 100 is replaced with a control unit 40. The calculation unit 41 and the storage unit 42 of the control unit 40 correspond to the calculation unit 31 and the storage unit 32 of the control unit 30, respectively. In addition to performing the same operations as the control unit 30, the control unit 40 is configured to be able to perform channel setting in response to a command signal INS_M that commands manual channel setting and is given by a user of the optical transceiver 200 or a device such as a host device connected to the optical transceiver 200.

[0072] Next, a manual channel setting process according to this embodiment will be described. Here, as in FIG. 2, it is assumed that optical transmission device 1 is provided with optical transceivers A1 to A25 having the same configuration as optical transceiver 200, and optical transmission device 2 is provided with optical transceivers B1 to B25 having the same configuration as optical transceiver 200.

[0073] As in the first embodiment, upon receiving the command signal INS, the optical transceivers A2 and B2 change the local channel information L, i.e., sweep the local channels while transmitting channel setting optical signals, thereby starting autonomous channel setting. However, in this embodiment, it is assumed that channel CH3 and channel CH4 are assigned as the transmit channels for the optical transceivers A2 and B2, respectively. Therefore, to manually set the channels after the autonomous channel setting has started, the user issues a command signal INS_M to the optical transceiver A2, specifying the channels to be used for transmission and reception.

[0074] The channel setting operation will be described below in order. Fig. 11 shows an example of a channel setting optical signal transmitted and received between the optical transceiver A2 and the optical transceiver B2 in the channel setting process in the second embodiment. Here, an example will be described in which the optical transceiver A2 and the optical transceiver B2 each transmit a channel setting signal once, and then a command signal INS_M is given to the optical transceiver A2 to perform manual channel setting. (1) SA1 / LA:CH1, RA:NONE 11, similar to the example in FIG. 8, optical transceiver A2 first transmits a channel setting optical signal SA1 for channel CH1, with local channel information LA set to channel CH1 and remote channel information RA set to null (NONE). In this example, channel CH1 is the channel used for transmission from optical transceiver A1 to optical transceiver B1. That is, the port for channel CH1 of optical multiplexer / demultiplexer M2 in optical transmission device 2 is connected to the receive port of optical transceiver B1. Therefore, the channel setting optical signal SA1 is blocked by optical multiplexer / demultiplexer M2 and does not reach optical transceiver B2.

[0075] (2)SB1 / LB:CH1,RB:NONE 8, optical transceiver B2 then transmits a channel setting optical signal SB1 for channel CH1, with local channel information LB set to channel CH1 and remote channel information RB set to null (NONE). Because the transmit port of optical transceiver A1 is connected to the port for channel CH1 of optical multiplexer / demultiplexer M1 in optical transmission device 1, the channel setting optical signal SB1 is blocked by optical multiplexer / demultiplexer M1 and does not reach optical transceiver A2. (3) INS_M input Here, the user issues a command signal INS_M to the optical transceiver A2 to assign channel CH3 as the transmission channel for the optical transceiver A2 and channel CH4 as the transmission channel for the optical transceiver B2. Upon receiving the command signal INS_M, the optical transceiver A2 stops autonomous channel setting, i.e., channel sweeping. (4) SA0 / LA:CH3, RA:CH4, state transition:EU→EK In response to the command signal INS_M, the optical transceiver A2 transmits a channel setting optical signal SA0 for channel CH3, with the local channel information LA set to channel CH3 and the remote channel information RA set to channel CH4. The channel setting optical signal SA0 for channel CH3 is received by the optical transceiver B2. At this time, the optical transceiver A2 detects the channel to be used for transmission and reception, and the state of the optical transceiver A2 transitions from EU to EK.

[0076] As in the case of FIG. 8, the optical transceiver B2 receives channel CH3 as local channel information LA and channel CH4 as remote channel information RA from the optical transceiver A2. The local channel information LA and remote channel information RA from the optical transceiver A2 are remote channel information RB and local channel information LB, respectively, to the optical transceiver B2. Therefore, the optical transceiver B2 fixes the local channel information LB to channel CH4 and the remote channel information RB to channel CH3. Fixing the local channel information LB and the remote channel information RB sets the transmission channel for the optical transceiver B2, so the optical transceiver B2 stops channel sweeping. This puts the optical transceiver B2 in a state (state EK) where it has detected the transmission channel of the partner optical transceiver A2 and a channel available for transmission from the optical transceiver B2 to the optical transceiver A2, and the state transitions from EU to EK.

[0077] (5) SB0 / LB: CH4, RB: CH3, state transition: EK → LE The optical transceiver B2 transmits a channel setting optical signal SB0 for channel CH4, with local channel information LB fixed to channel CH4 and remote channel information RB fixed to channel CH3. The channel setting optical signal SB0 for channel CH4 is received by the optical transceiver A2.

[0078] 8, the optical transceivers A2 and B2 can confirm that the local channel information LA of the optical transceiver A2 and the remote channel information RB of the optical transceiver B2 match on channel CH3, and that the local channel information LB of the optical transceiver B2 and the remote channel information RA of the optical transceiver A2 match on channel CH4. Therefore, the channels to be used for transmission and reception are determined, and the optical transceivers A2 and B2 transition to a state in which a connection is established (state LE: Link Established), and the channel setting process is terminated.

[0079] As a result, after the manual channel setting is completed, the optical transceiver A2 and the optical transceiver B2 can transmit and receive optical signals using the channels CH3 and CH4, as in the first embodiment.

[0080] As described above, with this configuration, even after starting autonomous channel setting, an optical transceiver can stop the autonomous channel setting by receiving a command signal INS_M and set the transmission channel and reception channel specified by the command signal INS_M. Furthermore, an optical transceiver that is the communication partner of the optical transceiver that received the command signal can also set the transmission channel and reception channel by receiving a channel setting optical signal from the optical transceiver that received the command signal INS_M.

[0081] From the perspective of a user of a system equipped with optical transceivers, the channel settings of the two optical transceivers can be easily performed manually by simply issuing a command signal to one of the two optical transceivers that transmits and receives optical signals, specifying the channel to be used for transmission and reception.

[0082] As a result, the channel setting operation can be completed quickly and preferentially by performing interrupt processing of the command signal INS_M by software, without requiring channel sweeping in autonomous channel setting. In the example of Fig. 11, it is possible to reduce the transmission and reception of channel setting optical signals SA2 to SA4 and SB2 to SB4 involved in channel sweeping compared to the example of Fig. 8, and it can be seen that the time required for channel setting can be shortened by the time required for transmitting and receiving the reduced channel setting optical signals.

[0083] Although the above description focuses on the optical transceivers A2 and B2, it goes without saying that the manual channel setting process can be similarly performed for the other optical transceivers A1, A3 to A25, B1, and B3 to B25.

[0084] In the above description, a command signal is sent to manually set the channels when both of the two optical transceivers transmitting and receiving optical signals are in the unknown state EU, where the transmit and receive channels to be set are unknown. However, this is merely an example. As shown in Figure 8, after autonomous channel setup begins, each of the two optical transceivers transmitting and receiving optical signals may be in a state PK where it has detected the transmit channel of the other optical transceiver, or in a state EK where it has detected the transmit channel of the other optical transceiver and a channel available for transmission to the other optical transceiver but the channel setup has not been established. Even in this case, by sending a command signal to one of the two optical transceivers transmitting and receiving optical signals, it is possible to stop the autonomous channel setup performed by the optical transceiver that received the command signal and manually set the channels to be used for transmission and reception. In addition, the optical transceiver that is the communication partner of the optical transceiver that received the command signal can also manually set the channel to be used for transmission and reception by receiving a channel setting optical signal (i.e., the channel setting optical signal SA0 or SB0 in Figures 8 and 11) from the optical transceiver that received the command signal.

[0085] Embodiment 3 In the first and second embodiments, the channel setting of two optical transceivers that transmit and receive optical signals has been described, but the signals that can be superimposed on the main signal, which is the data signal to be transmitted and received, can be not only the channel setting signals described above, but also control signals for the optical transceiver of the communication partner and the host device to which the optical transceiver of the communication partner is connected. In this embodiment, an optical transceiver that can superimpose a control signal on the main signal will be described.

[0086] 12 is a schematic diagram illustrating the configuration of an optical transceiver 300 according to the third embodiment. The optical transceiver 300 according to the third embodiment has a configuration in which the control unit 30 of the optical transceiver 100 is replaced with a control unit 50. The calculation unit 51 and the storage unit 52 of the control unit 50 correspond to the calculation unit 31 and the storage unit 32 of the control unit 30, respectively.

[0087] The optical transceiver 300 superimposes a control signal C1 onto a main signal MS1 to control the operation of the other party's optical transceiver or a host device to which the other party's optical transceiver is connected, and outputs the superimposed signal as an optical signal LS1. The optical transceiver 300 is also configured to receive an optical signal LS2, which is output from the other party's optical transceiver and in which a control signal C2 is superimposed on the main signal MS2, and to operate in accordance with the control signal C2. Note that the transmission and reception of the control signal is similar to the transmission and reception of the channel setting optical signal, and therefore will not be described here.

[0088] Next, transmission of a control signal and corresponding operations in this embodiment will be described. Fig. 13 shows a schematic diagram of an optical communication system according to the third embodiment and an example of transmission and reception of an optical signal. As in the first and second embodiments, optical transmission device 1 is provided with optical transceivers A1 to A25 having the same configuration as optical transceiver 300, and optical transmission device 2 is provided with optical transceivers B1 to B25 having the same configuration as optical transceiver 300.

[0089] The optical transceivers A1 to A25 installed in the optical transmission device 1 communicate with the other party through the optical transceivers A1 to A25, and are connected to a host device 3 that performs various processes required for the communication. The optical transceivers A1 to A25 and the host device 3 are connected by data communication lines DA1 to DA25, respectively, that exchange data signals modulated into main signals by each transceiver and transmitted, and data signals demodulated from received main signals, and are also connected by communication lines CA1 to CA25 that exchange electrical signals other than data signals.

[0090] The optical transceivers B1 to B25 installed in the optical transmission device 2 communicate with the other party through the optical transceivers B1 to B25 and are connected to a host device 4 that performs various processes required for the communication. The optical transceivers B1 to B25 and the host device 4 may be connected by data communication lines DB1 to DB25, respectively, that exchange data signals modulated into main signals by each transceiver and transmitted, and data signals demodulated from received main signals, and may also be connected by communication lines CB1 to CB25 that exchange electrical signals other than data signals.

[0091] For simplicity of explanation, an example will be described in which the control signal CS superimposed on the main signal is transmitted from the optical transceiver A2 to the optical transceiver B2.

[0092] First, we will explain the case where the optical transceiver of the other communication partner is controlled. Figure 14 schematically shows the signal flow when controlling the optical transceiver of the other communication partner in embodiment 3. The source optical transceiver A2 can instruct the other communication partner optical transceiver B2 to turn on / off the optical output, i.e., to stop or start transmitting the optical signal, by superimposing the control signal CS on the main signal MS_A2 and transmitting it. Note that the optical transceiver can output a control signal in response to receiving signals such as the command signal INS and command signal INS_M described above.

[0093] The optical transceiver A2 can also request information such as configuration parameters from the other party's optical transceiver B2 by superimposing a control signal CS on the main signal MS_A2 and transmitting it. Upon receiving the request, the optical transceiver B2 superimposes a response signal RES indicating the information it holds on the main signal MS_B2 and transmits it to the optical transceiver A2. The optical transceiver A2 receives the response signal RES, converts it into an electrical signal RES_E, and forwards it to the optical transmission device 1 and other devices as necessary. The requested information can be, for example, configuration information such as the transmit channel, receive channel, optical output, optical input level, transceiver temperature, laser status monitoring (wavelength monitor, laser temperature, laser current value), optical transceiver model name, and program version.

[0094] Next, we will explain the case of controlling the host device of the other communication partner. Figure 15 schematically shows the signal flow when controlling the host device to which the optical transceiver of the other communication partner is connected in embodiment 3. The optical transceiver A2 can also instruct the host device 4 to turn on or off communication processing to the host device 4 to which the optical transceiver B2 of the other communication partner is connected by sending a control signal CS. In this case, the optical transceiver A2 sends the control signal CS to the optical transceiver B2, and the optical transceiver B2 receives the control signal CS, converts it into a control signal CS_E, which is an electrical signal, and transfers it to the host device 4 via the communication line DB2. The host device 4 can stop and start communication processing in response to the control signal CS_E.

[0095] The optical transceiver A2 can also request information held by the host device 4 connected to the optical transceiver B2 by transmitting a control signal CS. In this case, the host device 4 outputs a response signal RES_E, an electrical signal indicating the information requested by the control signal CS_E, to the optical transceiver B2 via the communication line CB2. The optical transceiver B2 superimposes the response signal RES_E on the main signal MS_B2 as an optical signal RES and transmits it to the optical transceiver A2. The optical transceiver A2 receives the response signal RES, converts it into an electrical signal RES_E, and forwards it to the host device 3 or another device via the communication line DA2 as needed. The requested information can be, for example, configuration information such as the number of optical transceivers connected and the transmit and receive channels of each optical transceiver.

[0096] As described above, according to this configuration, by superimposing a control signal on a main signal from one of two optical transceivers that transmit and receive optical signals to the other optical transceiver of the communication partner, it is possible to control the operation of the optical transceiver of the communication partner and the host device to which the optical transceiver of the communication partner is connected.

[0097] The optical communication system shown in FIG. 13 and described in this embodiment is used, for example, in a fifth-generation mobile communication system (hereinafter referred to as 5G). In such systems, base stations equipped with optical transmission devices are often installed in relatively difficult-to-reach locations, such as in the mountains, on the rooftops of buildings, or in areas with railway tracks. In such cases, it is difficult for workers to reach the base stations, and workers with special skills are required. In contrast, with this configuration, an optical transceiver in a remote base station can transmit a control signal to a target optical transceiver to remotely control its operation. This enables the target optical transceiver or optical transmission device to perform a desired operation without dispatching a worker to the base station. This significantly reduces the number of personnel, costs, and time required for maintenance and inspection of optical transceivers and optical transmission devices.

[0098] Furthermore, it is known that 5G requires a relatively large number of base stations because the frequencies used for communication are higher than those used in previous mobile communication systems. Therefore, by performing remote control as in this configuration, even if many base stations are installed, the optical transmission equipment and optical transceivers in the base stations can perform the desired operations. This effectively suppresses the increase in personnel, costs, and time required for maintenance and inspection work due to the increase in base stations.

[0099] Embodiment 4 An optical transceiver according to the fourth embodiment will be described. The optical transceiver according to the fourth embodiment is configured to change the optical signals of the superimposed channel setting optical signal and control signal in conjunction with fluctuations in the optical intensity of the main signal, i.e., fluctuations in amplitude, when superimposing one or both of the channel setting optical signal and the control signal described in the above embodiments.

[0100] Hereinafter, for the sake of simplicity, the signal superimposed on the main signal will be referred to as a superimposed signal. This superimposed signal may include one or both of the channel setting optical signal and the control signal described in the above embodiment, as well as optical signals other than the main signal.

[0101] 16 is a schematic diagram illustrating the configuration of an optical transceiver 400 according to the fourth embodiment. The optical transceiver 400 according to the fourth embodiment has a configuration in which the wavelength-tunable optical transmitter 10 of the optical transceiver 100 is replaced with a wavelength-tunable optical transmitter 60, and the control unit 30 is replaced with a control unit 70. The calculation unit 71 and the storage unit 72 of the control unit 70 correspond to the calculation unit 31 and the storage unit 32 of the control unit 30, respectively.

[0102] The optical transceiver 400 superimposes the superimposed signal SP1 on the main signal MS1 and outputs the superimposed signal as an optical signal LS1. The optical transceiver 400 is also configured to receive an optical signal LS2, which is output from a communication partner optical transceiver and is formed by superimposing the superimposed signal SP2 on the main signal MS2, and to operate in response to the superimposed signal SP2.

[0103] 17 is a schematic diagram illustrating the configuration of a wavelength-tunable optical transmitter 60 according to the fourth embodiment. The wavelength-tunable optical transmitter 60 includes a driver 61 and an optical signal transmitter 62, which correspond to the driver 11 and the optical signal transmitter 12, respectively, in the wavelength-tunable optical transmitter 10. The drive signal DRV output from the driver 61 to the optical signal transmitter 62 includes a main signal modulation signal MOD_M, which is a signal for modulating the main signal, and an amplification control signal ACS, which controls the amplification operation of the optical signal amplifier 62C. The main signal modulation signal MOD_M is output based on a main signal IN, which is a data signal. The amplification control signal ACS can also be used to control the amplification factor of the optical signal amplifier 62C.

[0104] The optical signal transmitter 62 has an optical signal output unit 62A, an optical monitor unit 62B, and an optical signal amplifier unit 62C. The optical signal output unit 62A has a light source and an optical modulator, and modulates laser light in accordance with a main signal modulation signal MOD_M to output a main signal MS1. The optical monitor unit 62B is provided on the output side of the optical signal amplifier unit 62C, and monitors the output light of the optical signal amplifier unit 62C. The optical signal amplifier unit 62C amplifies the main signal MS1 output from the optical signal output unit 62A in accordance with an amplification control signal ACS. The optical signal amplifier unit 62C may be configured as a semiconductor optical amplifier (SOA).

[0105] That is, in this configuration, by providing a width control signal ACS to the optical signal amplifier 62C in accordance with the monitoring result of the intensity of the output light of the optical signal amplifier 62C by the optical monitor unit 62B, it is possible to perform an APC operation in which feedback control is performed so that the average value of the intensity of the output light of the optical signal amplifier 62C becomes a constant value.

[0106] Furthermore, in this configuration, as will be described later, the amplification control signal ACS can include a modulation signal for superimposing the superimposed signal SP1 on the main signal MS1 based on a control signal CON from the control unit 70. This allows the optical signal amplifying unit 62C to modulate the main signal MS1 according to the amplification control signal ACS into a signal having a waveform in which the amplitude transitions between two levels by amplitude shift keying (ASK) or phase shift keying (PSK), thereby superimposing the superimposed signal SP1 on the main signal MS1.

[0107] In this configuration, the monitor unit 62B monitors the amplitude of the optical signal LS1, which is output from the optical signal amplifier unit 62C and is obtained by superimposing the superimposed signal SP1 on the main signal MS1, and the average amplitude and optical intensity of the superimposed signal SP1 may be feedback-controlled according to the monitoring results.

[0108] In this embodiment, the superimposed signal is superimposed on the main signal by modulating the main signal using amplitude shift keying or phase shift keying to generate a signal having a waveform whose amplitude transitions between two levels. FIG. 18 schematically shows the waveform and eye pattern of the main signal before and after modulation. When the main signal is modulated, the superimposed signal appears as a staircase at the upper amplitude limit of the main signal (upper right panel of FIG. 18). Furthermore, to maintain signal quality, it is necessary to keep the amplitude of the superimposed signal within a certain range relative to the amplitude of the main signal. In eye patterns, which are commonly known as a method for evaluating signal quality, the amplitude of the superimposed signal appears as the variation in the signal locus depicted in the eye pattern, i.e., the width of the locus. In FIG. 18, when the main signal is not modulated, the upper locus of the eye pattern is similar to the other loci (reference U1 in FIG. 18). However, when the main signal is modulated, the amplitude of the main signal changes in a staircase-like manner, resulting in a thicker upper locus of the eye pattern (reference U2 in FIG. 16). If the upper trace of the eye pattern becomes thicker than the limit, the eye of the eye pattern (EYE in Figure 18) will narrow, leading to degradation of signal quality. Therefore, the amplitude of the superimposed signal must be controlled so as not to cause degradation of signal quality.

[0109] Furthermore, simply amplifying and modulating the main signal, as shown in Figure 18, increases the average signal strength after modulation by ΔAVE. However, the strength of the optical signal transmitted from the optical transceiver (hereinafter, this refers to the average optical signal strength AVE) must be kept constant by APC (Auto Power Control) operation in order to maintain the transmission quality of the optical signal.

[0110] Therefore, it is conceivable to perform modulation so that the amplitude of the main signal is increased or decreased in a stepwise manner around the upper limit of the amplitude of the main signal before modulation. Fig. 19 shows an example (hereinafter referred to as a comparative example) in which a main signal is modulated and a superimposed signal is superimposed. In this example, the optical signal output from the optical signal amplifier 62C is modulated to the upper limit of the amplitude A of the optical signal whose optical intensity has been adjusted to a target value by APC operation. APCThe resulting optical signal is modulated as a signal whose amplitude increases or decreases by a width ΔA around the center of the optical signal. This allows the superimposed signal to be superimposed on the main signal without changing the average intensity of the optical signal before and after modulation.

[0111] When performing such modulation, the superimposed signal can be superimposed on the main signal by simply modulating the gain of the optical signal amplifier 62C so that the amplitude increases or decreases at a fixed modulation index (hereinafter, this modulation method will be referred to as a comparative example). Below, the comparative example will be described with reference to the configuration of the transceiver 400 described above. Here, the gain for realizing the target optical intensity by APC operation is α, the modulation index for superimposing the superimposed signal is β, and the amplitude of the main signal MS1 input to the optical signal amplifier 62C is A. IN In this case, the amplitude of the superimposed signal superimposed on the optical signal output from the optical signal amplifier 62C is α(1+β)·A IN and α(1-β)·A IN In the APC operation, the amplification factor α is adjusted according to the optical intensity of the optical signal output from the optical signal amplifier 62C, so that the amplitude α·β1·P of the superimposed optical signal IN (The above-mentioned ΔA) is the amplification factor α and the intensity P of the main signal MS1 input to the optical signal amplifier 62C. IN It changes depending on the

[0112] Generally, the temperature inside an optical transceiver fluctuates due to factors such as the environment in which the optical transceiver is installed and heat generated by components installed in the optical transceiver. As a result, temperature characteristics are generated in the light source, optical modulator, optical amplifier, and other components provided to output an optical signal. Furthermore, the characteristics of the optical transceiver fluctuate due to factors such as aging. It is known that when such fluctuations in characteristics, such as temperature characteristics and aging, occur, the intensity of the optical signal output from the optical signal amplifier 62C also fluctuates even if the same value of the amplification control signal ACS is applied to the optical signal amplifier 62C, in other words, even if the same current value is applied to the amplification control signal ACS.

[0113] In particular, in recent years, some or all of the wavelength-tunable optical transmitters have been fabricated using silicon photonics technology. It is known that the optical characteristics of elements fabricated using silicon photonics technology are susceptible to changes in temperature, and it is therefore necessary to appropriately compensate for the temperature characteristics.

[0114] Therefore, in optical transceivers, in order to compensate for fluctuations in characteristics such as temperature characteristics and aging, the strength of the optical signal output from the optical signal amplifier is monitored and APC control is performed to keep the strength of the optical signal constant.As a result, when the modulation method according to the comparative example is used, the amplitude of the superimposed signal fluctuates due to fluctuations in characteristics.

[0115] 20 shows a change in the amplitude of the superimposed signal in the comparative example when the gain increases due to a characteristic fluctuation of the optical transceiver. IN When the amplitude α·β1·P of the superimposed optical signal is reduced, the amplification factor α of the optical signal amplifier 62C is increased by the APC operation to compensate for this. IN Since the amplitude ΔA1 of the superimposed signal when the characteristics fluctuate becomes larger than the amplitude ΔA0 of the superimposed signal before the characteristics fluctuate. In this case, the eye of the eye pattern is narrowed by the superimposed signal with increased amplitude, resulting in degradation of signal quality. In addition, the amplitude of the superimposed signal to be transmitted changes, leading to degradation of the signal quality of the superimposed signal.

[0116] 21 shows a change in the amplitude of the superimposed signal in the comparative example when the gain is reduced due to a characteristic fluctuation of the optical transceiver. IN When the amplitude α·β1·P of the superimposed optical signal is increased, the amplification factor α in the optical signal amplifier 62C is reduced by the APC operation to compensate for this. INTherefore, the amplitude ΔA2 of the superimposed signal when the characteristics fluctuate becomes smaller than the amplitude ΔA0 of the superimposed signal before the characteristics fluctuate. In this case, although the eye of the eye pattern does not narrow, the signal quality of the superimposed signal deteriorates.

[0117] Therefore, as will be described below, optical transceiver 400 according to this embodiment controls optical output amplifier 62C by APC operation so as to maintain constant the intensity of the optical signal output from optical output amplifier 62C and the amplitude of the superimposed signal.

[0118] The amplitude control of the superimposed signal in the optical transceiver 400 will be described below. The driver 61 controls the optical signal amplifier 62C so that the amplitude of the superimposed signal has a constant ratio to the amplitude of the main signal whose intensity has been adjusted to a constant value by the APC operation. APC , the amplitude A of the main signal MS1 to determine the amplitude of the superimposed signal SP1 APC When the ratio (modulation depth) by which the signal is multiplied is γ, the optical signal output from the optical signal amplifier 62C in this embodiment has an amplitude upper limit A of the optical signal whose optical intensity has been adjusted to a target value by the APC operation. APC (A APC = α A IN ) and A APC +γ·A APC and A APC -γ·A APC The amplitude of the signal changes stepwise between γ and γ. Note that γ is an arbitrary value greater than 0 and less than 1 (0<γ<1).

[0119] The upper limit A of the amplitude of the optical signal whose optical intensity has been adjusted to the target value by APC operation APCis maintained constant, the amplitude of superimposed signal SP1 remains unchanged even if the characteristics of the optical transceiver fluctuate. Figure 22 shows a signal waveform when the amplitude of superimposed signal SP1 is controlled in transceiver 400 according to the amplitude of amplified main signal MS1. As shown in Figure 22, even if the amplification factor α fluctuates, the amplitude of superimposed signal SP1 remains unchanged, so signal quality can be maintained without affecting the eye pattern of the optical signal output from the optical signal amplifier.

[0120] The ratio γ can be set to a value within a range in which the transmission quality of the main signal can be ensured. That is, the ratio γ is set to a lower limit value γ L and upper limit γ H As an example of the range of the ratio γ in which the transmission quality of the main signal can be ensured, the lower limit value γ L is 2% (0.02), and the upper limit γ H is 10% (0.1) (0.02≦γ≦0.1). A typical value of γ is, for example, 7.5% (0.075).

[0121] As described above, according to this configuration, when a superimposed signal is superimposed on a main signal, the amplitude of the superimposed signal can be set to a predetermined ratio with respect to the amplitude of the main signal whose intensity has been adjusted by APC operation, and the superimposed signal can be superimposed on the main signal without affecting the transmission quality of the signal.

[0122] The amplitude control of the superimposed signal described in this embodiment can be performed at any timing. The amplitude control of the superimposed signal may be performed, for example, as an initial setting operation when the optical transceiver is installed, or after changing the transmission settings of the optical transceiver, such as changing the channel of the optical signal to be transmitted or changing the output value of the main signal. Furthermore, the amplitude control of the superimposed signal may be performed periodically after the optical transceiver starts operating, or may be performed continuously. It goes without saying that the timing at which the driver performs control can be easily controlled by the controller.

[0123] Fifth embodiment An optical transceiver according to a fifth embodiment will be described. In the fourth embodiment, the amplitude of the superimposed signal is adjusted by referring to the monitoring result of the amplitude of the optical signal, whereas the optical transceiver according to this embodiment is configured to adjust the amplitude of the superimposed signal based on information given in advance.

[0124] 23 is a schematic diagram illustrating the configuration of an optical transceiver 500 according to the fifth embodiment. The optical transceiver 500 according to the fifth embodiment has a configuration in which the control unit 70 of the optical transceiver 400 is replaced with a control unit 80. The calculation unit 81 and the storage unit 82 of the control unit 80 correspond to the calculation unit 71 and the storage unit 72 of the control unit 70, respectively. The optical transceiver 500 also includes a temperature sensor 510 for measuring the internal temperature of the optical transceiver 500. The temperature sensor 510 can be installed at any position in the optical transceiver 500, and may be installed inside the wavelength-tunable optical transmitting unit 50, for example. The temperature sensor 510 outputs a temperature detection signal TMP indicating the measured temperature to the control unit 80.

[0125] In order to compensate for the influence of fluctuations in the amplitude of the optical signal due to the temperature characteristics of the light source, optical modulator, optical amplifier, etc., the storage unit 82 stores, as table information TAB_1, for example, the value of the amplification control signal ACS to be provided to the optical signal amplifier 62C in accordance with the temperature measured by the temperature sensor 510. The calculation unit 81 references the table information TAB_1 in the storage unit 82 based on the temperature indicated by the temperature detection signal TMP, and instructs the drive unit 61 on the value of the amplification control signal ACS to be output. In response to this, the drive unit 61 outputs the amplification control signal ACS to the optical signal amplifier 62C, making it possible to adjust the amplitude of the superimposed signal within an appropriate range even when there is a change in temperature.

[0126] As mentioned above, in recent years, some or all of the components of wavelength-tunable optical transmitters have been fabricated using silicon photonics technology. It is known that the optical characteristics of elements fabricated using silicon photonics technology are susceptible to changes in temperature, and it is therefore considered important to control the amplitude of the superimposed signal according to temperature.

[0127] Although the amplitude of the superimposed signal is adjusted in accordance with temperature, the amplitude of the superimposed signal may also be adjusted in accordance with changes in the optical transceiver over time. In this case, the storage unit 82 stores, for example, table information TAB_2, the value of the amplification control signal ACS to be provided to the optical signal amplifier 62C in accordance with the time elapsed since the optical transceiver began operation. The calculation unit 81 may be configured to write the time elapsed since the optical transceiver began operation to the storage unit 82 and read it from the storage unit 82 as needed. The calculation unit 81 references the table information TAB_2 in the storage unit 82 based on the time elapsed since the optical transceiver began operation, and instructs the driver 61 to output the value of the amplification control signal ACS. In response to this, the driver 61 outputs the amplification control signal ACS to the optical signal amplifier 62C, thereby making it possible to adjust the amplitude of the superimposed signal to an appropriate value even when changes in the optical transceiver occur over time.

[0128] As described above, according to this configuration, by referring to information given in advance, it is possible to adjust the amplitude of the superimposed signal SP1 to within a range of a predetermined ratio with respect to the amplitude of the main signal MS1.

[0129] The amplitude control of the superimposed signal according to the temperature and the amplitude control of the superimposed signal according to the elapsed time may be implemented independently in the optical transceiver, or may be implemented in combination in the optical transceiver.

[0130] Furthermore, the information given in advance is not limited to the above, and may be information linked to something other than temperature or elapsed time.

[0131] Sixth embodiment An optical transceiver according to a sixth embodiment will be described. The optical transceiver according to the sixth embodiment is configured to apply Manchester coding as a modulation method when modulating a main signal and superimposing a superimposed signal. It goes without saying that Manchester coding can be applied to the modulation of superimposed signals, i.e., channel setting optical signals, control signals, and other superimposed signals, in the optical transceivers described in the above embodiments.

[0132] A Manchester-encoded signal will now be described. Fig. 24 shows the relationship between signals and bits in Manchester encoding. In Manchester encoding, one bit can be transmitted per period T, and the bit is represented by a signal transition in the middle of period T. In this embodiment, as shown in Fig. 24, a signal falling from HIGH to LOW represents a bit "0," and a signal rising from LOW to HIGH represents a bit "1."

[0133] In this embodiment, bit synchronization is performed by transmitting a superimposed signal for bit synchronization in order to accurately receive a Manchester-encoded superimposed signal. In this embodiment, to perform bit synchronization, a superimposed signal for bit synchronization is transmitted when transmitting an optical signal from a transmitting optical transceiver. FIG. 25 shows an example of an optical signal transmitted by a transmitting optical transceiver. As shown in FIG. 25, the transmitting optical transceiver first transmits a frame (bit synchronization frame) consisting of a superimposed signal for bit synchronization, and then transmits a frame (frame synchronization frame) for frame synchronization. These frames correspond to the header information OH in FIG. 3. Then, a frame containing a command signal including a command to the receiving side is transmitted. The frame containing the command signal corresponds to the local channel information L and remote channel information R in FIG. 3. Each frame is composed of a continuous bit string.

[0134] When an optical transceiver receives a superimposed signal for bit synchronization, it detects signal transitions at the timing of transitions of the superimposed signal in order to decode the bits represented by the superimposed signal.

[0135] FIG. 26 shows an example of a superimposed signal for bit synchronization. The superimposed signal for bit synchronization in FIG. 26 corresponds to the detection signal DET output from the amplifier unit 21 to the control unit 70 in FIG. 17. The level of the Manchester-encoded superimposed signal always transitions at the center of the period representing the bits. However, depending on the bit string represented by the superimposed signal, there may be a mixture of cases where the level transitions at the boundary of the period (timing a in FIG. 26) and cases where there is no transition (timings b1 and b2 in FIG. 26). When there is no level transition, there may be cases where the level remains LOW (timing b1 in FIG. 26) and cases where the level remains HIGH (timing b2 in FIG. 26).

[0136] When the optical transceiver starts detecting transitions in the superimposed signal for bit synchronization, it is unclear whether the detected level transition is at the correct timing, i.e., whether it is detected in the center of the period T. Therefore, depending on the detection timing, it may detect a level transition at a period boundary. In this case, a level transition other than the one representing the bit represented by the superimposed signal is detected, and it is necessary to change the detection timing of the level transition to the correct timing. Therefore, in this embodiment, the bit synchronization operation described below is performed to ensure that the detection timing of the level transition is correct.

[0137] The optical signal receiving unit of the receiving optical transceiver performs bit synchronization using the bit synchronization frame to establish a state in which each bit represented by the superimposed signal can be accurately decoded. Then, it establishes frame synchronization using the frame synchronization frame. This allows the command signal contained in the frame containing the command signal to be subsequently received to be accurately decoded.

[0138] The procedure of the bit synchronization operation according to the sixth embodiment will be described below. Fig. 27 is a flowchart showing the procedure of the bit synchronization operation according to the sixth embodiment.

[0139] Step ST1 Upon receiving the bit synchronization superimposed signal, the optical signal receiving section of the receiving optical transceiver detects a level transition in the bit synchronization frame at any timing.

[0140] Step ST2 After detecting a level transition in the bit synchronization frame at an arbitrary timing, the detection of a level transition of the superimposed signal continues at the timing of each period T of Manchester encoding.

[0141] Step ST3 If, as a result of continuing to detect a transition in the level of the superimposed signal within the bit synchronization frame, there is a timing at which the level of the superimposed signal does not transition at the timing of each period T, the detection timing is changed so that the timing at which the transition in the level of the superimposed signal is detected is delayed by 1 / 2 of the period T.

[0142] Step ST4 If, as a result of continuing to detect the level transition of the superimposed signal within the bit synchronization frame, the level of the superimposed signal transitions at all timings for each period T, the timing for detecting the level transition of the superimposed signal is maintained as is.

[0143] Next, the relationship between the bit synchronization operation according to the above procedure and the detection timing of signal level transitions will be described. FIG. 28 shows a first example of bit synchronization operation. When the optical signal receiving unit receives a superimposed signal for bit synchronization, it starts detecting level transitions of the superimposed signal. At this time, level transitions of the superimposed signal can occur not only in the center of the period T but also at the boundaries of the period T. Therefore, on the optical signal receiving unit side, a time arrives when the level of the superimposed signal does not transition at the boundaries of the period T (timing tA1 in FIG. 28). In this case, since the timing at which the level transition of the superimposed signal is detected coincides with the boundaries of the period T, the optical signal receiving unit delays the detection timing of the level transition of the superimposed signal by 1 / 2 the period T (step ST3 in FIG. 28). In FIG. 28, the detection timing is changed from timing tA2, which is the period T after timing tA1, to timing tA3, which is delayed by 1 / 2 the period T. As a result, the timing at which the level transition of the superimposed signal is detected coincides with the center of the period T (timing tA3 in FIG. 28), making it possible to accurately detect the bits represented by the superimposed signal.

[0144] In the above description, in step ST3, the optical signal receiving unit changes the timing at which it detects a level transition of the superimposed signal to timing tA3, delaying it from timing tA2 by 1 / 2 of the period T. However, this is merely an example, and the optical signal receiving unit may change the timing at which it detects a level transition of the superimposed signal to a timing delayed by 1 / 2 of the period T from timing tA1, at which it detected a deviation in the detection of the level transition of the superimposed signal. In this case, too, it is possible to make the timing at which it detects the level transition of the superimposed signal coincide with the center of the period T.

[0145] Next, a second example of bit synchronization operation is shown in Fig. 29. When the optical signal receiving unit starts detecting level transitions in the superimposed signal for bit synchronization, it may detect level transitions in the center of period T from the beginning (timing tB in Fig. 29, step ST1 in Fig. 27). In this case, even if detection of level transitions for each period T continues (step ST2 in Fig. 27), level transitions will be detected in the center of period T for each period T. In this case, since the timing at which the level transitions of the superimposed signal have already been detected coincides with the center of period T, the detection timing of the level transitions of the superimposed signal is maintained as is after detection within the bit synchronization frame is completed (step ST4 in Fig. 27).

[0146] As described above, with this configuration, when a superimposed signal for bit synchronization containing a bit string consisting of successive different bits is received, the optical signal receiving unit can automatically and accurately read the bits represented by the superimposed signal for bit synchronization using a simple configuration and processing.

[0147] The superposition of the superposition signal onto the main signal by Manchester encoding as described in this embodiment is not limited to application to the optical transceivers described in the first to fifth embodiments, but can also be applied to other optical transceivers.

[0148] Other embodiments The configurations according to the above-described embodiments are not limited to those described above and may be modified as appropriate without departing from the spirit of the invention. For example, the optical transmission device may be connected to various networks including trunk routes and branch routes, in addition to the network shown in FIG.

[0149] The number of optical transceivers and the number of channels provided in the optical transmission device are merely examples, and any number of optical transceivers and any number of channels may be provided.

[0150] In the above-described embodiment, it has been described that wavelength multiplexed signals are transmitted between optical transmission devices, but it goes without saying that various multiplexing methods other than wavelength multiplexing can be applied to the transmitted optical signals, and various modulation methods can be applied.

[0151] The configuration of the optical transceiver described above is simplified in order to explain the optical transceiver according to the above embodiment, and it goes without saying that it may include various components, such as a CDR (Clock Data Recovery) unit.

[0152] In the above description, an example has been described in which an optical signal obtained by on / off modulation is used as the channel setting optical signal, but an optical signal obtained by phase shift keying other than on / off modulation may also be used as the channel setting optical signal.

[0153] In the above-described embodiments, the present invention has been described mainly as a hardware configuration, but this is not limited thereto. The control of the wavelength-tunable optical transmitter and wavelength-tunable optical receiver by the controller and the channel setting process can also be realized by having a CPU (Central Processing Unit) execute a computer program. In this case, the arithmetic unit of the controller may be configured as a CPU. The program includes instructions (or software code) that, when loaded into a computer, cause the computer to execute one or more functions described in the above-described embodiments. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. Examples of non-transitory computer-readable media or tangible storage media include, but are not limited to, random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drives (SSD), or other types of storage technologies, such as compact disc (CD)-ROM, digital versatile disc (DVD), Blu-ray disc, or other types of optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage, or other magnetic storage devices. The program may be transmitted by a transitory computer-readable medium or a communication medium. Examples of transitory computer-readable media or tangible storage media may include, but are not limited to, electrical, optical, acoustic, or other forms of propagated signals.

[0154] The memory unit of the control unit can be any of various memory devices capable of writing and reading information, such as RAM, flash memory, SSD, optical disk memory device, magnetic cassette, magnetic tape, and magnetic disk memory device.

[0155] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the invention. [Explanation of symbols]

[0156] 1, 2 Optical transmission equipment 3, 4 Host device 10, 60 Wavelength tunable optical transmitter 11 Drive unit 12 Optical signal transmitter 20 Tunable wavelength optical receiver 21 Amplification section 22 Optical signal receiving unit 30, 40, 50, 70, 80 Control section 31, 41, 51, 71, 81 Arithmetic section 32, 42, 52, 72, 82 storage section 61 Drive unit 62 Optical signal transmitter 62A Optical signal output section 62B Optical monitor unit 62C Optical signal amplifier 100, 200, 300, 400, 500, A1~A25, B1~B25 Optical Transceiver 610 Temperature Sensor 1000 Optical Communication Systems AMP Optical Amplifier BS1, BS2 terminal station C1, C2 optical cables CA1~CA25, CB1~CB25 data communication lines CS, CS_E control signals CON control signal DAT output signal DET detection signal DRV drive signal DA1~DA25, DB1~DB25 data communication lines IN main signal INS, INS_M command signal L, LA, LB local channel information LS1, LS2 optical signal M1, M2 optical multiplexer / demultiplexer MS, MS1, MS2, MS_A2, MS_B2 Main signal MOD_M Main signal modulation signal ACS Amplification Control Signal MON monitor signal OH header information OUT Output signal R, RA, RB Remote channel information RES, RES_E response signal S, S1, S2, SA, SA0 to SA4, SB, SB0 to SB4 Optical signals for channel setting SP1, SP2 superimposed signal TAB_1, TAB_2 table information TMP Temperature detection signal

Claims

1. an optical transmitter that superimposes an optical signal for issuing a command to another optical transceiver on a first main signal that is an optical signal for transmitting communication data to the other optical transceiver, and outputs the superimposed optical signal as a first optical signal; an optical receiving unit that receives a second optical signal from the other optical transceiver; a control unit that controls the optical transmitting unit and the optical receiving unit, The optical transmitter unit a first superimposed signal, which is the optical signal superimposed on the first main signal, is superimposed on the first main signal by modulating the first main signal by amplitude shift keying to a signal having a waveform whose amplitude transitions between two levels; controlling the amplitude of the first superimposed signal based on a value obtained by multiplying the amplitude of the first main signal by a predetermined ratio; an upper limit value of the amplitude of the first superimposed signal is a value obtained by adding the amplitude of the first main signal and a value obtained by multiplying the amplitude of the first main signal by the predetermined ratio; and a lower limit value of the amplitude of the first superimposed signal is a value obtained by subtracting a value obtained by multiplying the amplitude of the first main signal by the predetermined ratio from the amplitude of the first main signal; The optical transmitter unit an optical signal output unit that outputs the first main signal; an optical signal amplifier that amplifies the first main signal output from the optical signal output unit; an optical monitoring unit that monitors the first optical signal output from the optical signal amplifier; a driver that drives the optical signal output unit and the optical signal amplifier unit, The drive unit is controlling the optical signal amplifier unit according to the monitoring result of the optical signal output by the optical monitoring unit so that the average value of the intensity of the optical signal output from the optical signal amplifier unit is maintained constant, and so that the first main signal is modulated by amplitude shift keying into a signal having a waveform whose amplitude transitions between two levels and so that the first superimposed signal is superimposed on the first main signal; Optical transceiver.

2. An optical transmitting unit that superimposes an optical signal for issuing a command to another optical transceiver on a first main signal, which is an optical signal for transmitting communication data to the other optical transceiver, and outputs the superimposed optical signal as a first optical signal; an optical receiving unit that receives a second optical signal from the other optical transceiver; a control unit that controls the optical transmitting unit and the optical receiving unit; a temperature sensor that measures the temperature of the optical transceiver; The optical transmitter unit a first superimposed signal, which is the optical signal superimposed on the first main signal, is superimposed on the first main signal by modulating the first main signal by amplitude shift keying to a signal having a waveform whose amplitude transitions between two levels; controlling the amplitude of the first superimposed signal based on a value obtained by multiplying the amplitude of the first main signal by a predetermined ratio; an upper limit value of the amplitude of the first superimposed signal is a value obtained by adding the amplitude of the first main signal and a value obtained by multiplying the amplitude of the first main signal by the predetermined ratio; and a lower limit value of the amplitude of the first superimposed signal is a value obtained by subtracting a value obtained by multiplying the amplitude of the first main signal by the predetermined ratio from the amplitude of the first main signal; The optical transmitter unit an optical signal output unit that outputs the first main signal; an optical signal amplifier that amplifies the first main signal output by the optical signal output unit to superimpose the first superimposed signal on the first main signal; a driver that drives the optical signal output unit and the optical signal amplifier unit, the control unit stores in advance first information linking the temperature of the optical transceiver with a command to be given to the drive unit; the control unit refers to the first information in accordance with the temperature measured by the temperature sensor and issues a first command to the drive unit; the driver controls the optical signal amplifier in response to the given first command so that an average value of intensity of the optical signal output from the optical signal amplifier is maintained constant, and so that the first main signal is modulated by amplitude shift keying into a signal having a waveform whose amplitude transitions between two levels, and so that the first superimposed signal is superimposed. Optical transceiver.

3. the control unit stores in advance second information that associates an elapsed time since the start of operation of the optical transceiver with a command to be given to the drive unit; the control unit refers to the second information in accordance with the elapsed time and issues a second command to the drive unit; the driver controls the optical signal amplifier in response to the second command given thereto so that an average value of intensity of the optical signal output from the optical signal amplifier is maintained constant, and so that the first main signal is modulated by amplitude shift keying into a signal having a waveform whose amplitude transitions between two levels, and so that the first superimposed signal is superimposed on the first main signal.

3. The optical transceiver according to claim 2.

4. An optical transmitting unit that superimposes an optical signal for issuing a command to another optical transceiver on a first main signal, which is an optical signal for transmitting communication data to the other optical transceiver, and outputs the superimposed optical signal as a first optical signal; an optical receiving unit that receives a second optical signal from the other optical transceiver; a control unit that controls the optical transmitting unit and the optical receiving unit, The optical transmitter unit a first superimposed signal, which is the optical signal superimposed on the first main signal, is superimposed on the first main signal by modulating the first main signal by amplitude shift keying to a signal having a waveform whose amplitude transitions between two levels; controlling the amplitude of the first superimposed signal based on a value obtained by multiplying the amplitude of the first main signal by a predetermined ratio; an upper limit value of the amplitude of the first superimposed signal is a value obtained by adding the amplitude of the first main signal and a value obtained by multiplying the amplitude of the first main signal by the predetermined ratio; and a lower limit value of the amplitude of the first superimposed signal is a value obtained by subtracting a value obtained by multiplying the amplitude of the first main signal by the predetermined ratio from the amplitude of the first main signal; The optical transmitter unit an optical signal output unit that outputs the first main signal; an optical signal amplifier that amplifies the first main signal output by the optical signal output unit to superimpose the first superimposed signal on the first main signal; a driver that drives the optical signal output unit and the optical signal amplifier unit, the control unit stores in advance information linking an elapsed time since the start of operation of the optical transceiver with a command to be given to the drive unit; the control unit refers to the information in accordance with the elapsed time and issues a command to the drive unit; the driver controls the optical signal amplifier in response to the given command so that the average value of the intensity of the optical signal output from the optical signal amplifier is maintained constant, and so that the first main signal is modulated by amplitude shift keying into a signal having a waveform whose amplitude transitions between two levels, and so that the first superimposed signal is superimposed. Optical transceiver.

5. the first superimposed signal is superimposed on the first primary signal by amplitude shift keying the first primary signal using Manchester encoding; 5. The optical transceiver according to claim 1.

6. the second optical signal is an optical signal on which a second superimposition signal, which is an optical signal for issuing a command to the optical transceiver, is superimposed, the second optical signal being obtained by modulating a second main signal, which is an optical signal corresponding to communication data, into a signal having a waveform in which the amplitude transitions between two levels by amplitude shift keying using Manchester coding; The optical receiving unit refers to synchronization information included in the second superimposed signal, After starting to detect a transition in the level of the second superimposed signal, the level of the second superimposed signal is detected at a timing corresponding to each period of Manchester encoding in the synchronization information; When there is a timing at which the level of the second superimposed signal does not change during the detection of the level at the timing of each period, the timing at which the transition of the level of the second superimposed signal is detected is delayed by 1 / 2 of the period; When there is no timing at which the level of the second superimposed signal does not change during the detection of the level at the timing for each period, the timing for detecting the transition of the level of the second superimposed signal is maintained; detecting a level transition of the second superimposed signal at the determined timing; 5. The optical transceiver according to claim 1.

7. An optical transmitting unit that superimposes an optical signal for issuing a command to another optical transceiver on a first main signal, which is an optical signal for transmitting communication data to the other optical transceiver, and outputs the superimposed optical signal as a first optical signal; an optical receiving unit that receives a second optical signal from the other optical transceiver; a control unit that controls the optical transmitting unit and the optical receiving unit, The optical transmitter unit a first superimposed signal, which is the optical signal superimposed on the first main signal, is superimposed on the first main signal by modulating the first main signal by amplitude shift keying to a signal having a waveform whose amplitude transitions between two levels; controlling the amplitude of the first superimposed signal based on a value obtained by multiplying the amplitude of the first main signal by a predetermined ratio; the second optical signal is an optical signal on which a second superimposition signal, which is an optical signal for issuing a command to the optical transceiver, is superimposed, the second optical signal being obtained by modulating a second main signal, which is an optical signal corresponding to communication data, into a signal having a waveform whose amplitude transitions between two levels by amplitude shift keying using Manchester coding; The optical receiving unit refers to synchronization information included in the second superimposed signal, After starting to detect a transition in the level of the second superimposed signal, the level of the second superimposed signal is detected at a timing corresponding to each period of Manchester encoding in the synchronization information; When there is a timing at which the level of the second superimposed signal does not change during the detection of the level at the timing of each period, the timing at which the transition of the level of the second superimposed signal is detected is delayed by 1 / 2 of the period; When there is no timing at which the level of the second superimposed signal does not change during the detection of the level at the timing for each period, the timing for detecting the transition of the level of the second superimposed signal is maintained; detecting a level transition of the second superimposed signal at the determined timing; Optical transceiver.

8. The second superimposed signal is a bit synchronization frame that is the synchronization information included in the second superimposed signal; a frame synchronization frame used for frame synchronization after being bit-synchronized by the bit synchronization frame; a command frame including information indicating a command to the optical transceiver; 8. The optical transceiver according to claim 6 or 7.

9. two opposing optical transmission devices each having a plurality of optical transceivers and a first optical multiplexer / demultiplexer that multiplexes and outputs optical signals output by the plurality of optical transceivers and demultiplexes received optical signals to the plurality of optical transceivers according to channels; an optical cable connecting the two opposing optical transmission devices, The optical transceiver of one of the optical transmission devices includes: an optical transmitter that superimposes an optical signal for issuing a command to another optical transceiver of another optical transmission device on a main signal that is an optical signal for transmitting communication data to the other optical transceiver, and outputs the superimposed optical signal; an optical receiving unit that receives an optical signal from the other optical transceiver; a control unit that controls the optical transmitting unit and the optical receiving unit, The optical transmitter unit the superimposed signal, which is the optical signal superimposed on the main signal, is superimposed on the main signal by modulating the main signal into a signal having a waveform whose amplitude transitions between two levels using amplitude shift keying; controlling the amplitude of the superimposed signal based on a value obtained by multiplying the amplitude of the main signal by a predetermined ratio; the upper limit of the amplitude of the superimposed signal is a value obtained by adding the amplitude of the main signal to a value obtained by multiplying the amplitude of the main signal by the predetermined ratio, a lower limit value of the amplitude of the superimposed signal is a value obtained by subtracting a value obtained by multiplying the amplitude of the main signal by the predetermined ratio from the amplitude of the main signal; The optical transmitter unit an optical signal output unit that outputs the main signal; an optical signal amplifier that amplifies the main signal output from the optical signal output unit; an optical monitor unit that monitors the optical signal output from the optical signal amplifier unit; a driver that drives the optical signal output unit and the optical signal amplifier unit, The drive unit is and controlling the optical signal amplifier according to the monitoring result of the optical signal output by the optical signal amplifier by the optical monitoring unit so that the average value of the intensity of the optical signal output from the optical signal amplifier is maintained constant, and so that the main signal is modulated by amplitude shift keying into a signal having a waveform whose amplitude transitions between two levels and the superimposed signal is superimposed. Optical communication system.

10. an optical transmitter that superimposes an optical signal for issuing a command to another optical transceiver on a main signal that is an optical signal for transmitting communication data to the other optical transceiver, and outputs the superimposed optical signal; an optical receiver that receives the optical signal from the other optical transceiver; and a controller that controls the optical transmitter and the optical receiver, the superimposed signal, which is the optical signal superimposed on the main signal, is superimposed on the main signal by modulating the main signal into a signal having a waveform whose amplitude transitions between two levels using amplitude shift keying; controlling the amplitude of the superimposed signal based on a value obtained by multiplying the amplitude of the main signal by a predetermined ratio; the upper limit of the amplitude of the superimposed signal is a value obtained by adding the amplitude of the main signal to a value obtained by multiplying the amplitude of the main signal by the predetermined ratio, a lower limit value of the amplitude of the superimposed signal is a value obtained by subtracting a value obtained by multiplying the amplitude of the main signal by the predetermined ratio from the amplitude of the main signal; The optical transmitter unit an optical signal output unit that outputs the main signal; an optical signal amplifier that amplifies the main signal output from the optical signal output unit; an optical monitor unit that monitors the optical signal output from the optical signal amplifier unit; a driver that drives the optical signal output unit and the optical signal amplifier unit, The drive unit is and controlling the optical signal amplifier according to the monitoring result of the optical signal output by the optical signal amplifier by the optical monitoring unit so that the average value of the intensity of the optical signal output from the optical signal amplifier is maintained constant, and so that the main signal is modulated by amplitude shift keying into a signal having a waveform whose amplitude transitions between two levels and the superimposed signal is superimposed. A method for controlling an optical transceiver.

11. Two opposing optical transmission devices each having a plurality of optical transceivers and a first optical multiplexer / demultiplexer that multiplexes and outputs optical signals output by the plurality of optical transceivers and demultiplexes received optical signals to the plurality of optical transceivers according to channels; an optical cable connecting the two opposing optical transmission devices, The optical transceiver of one of the optical transmission devices includes: an optical transmitter that superimposes an optical signal for issuing a command to another optical transceiver of another optical transmission device on a main signal that is an optical signal for transmitting communication data to the other optical transceiver, and outputs the superimposed optical signal; an optical receiving unit that receives an optical signal from the other optical transceiver; a control unit that controls the optical transmitting unit and the optical receiving unit; a temperature sensor that measures the temperature of the optical transceiver; The optical transmitter unit the superimposed signal, which is the optical signal superimposed on the main signal, is superimposed on the main signal by modulating the main signal into a signal having a waveform whose amplitude transitions between two levels using amplitude shift keying; controlling the amplitude of the superimposed signal based on a value obtained by multiplying the amplitude of the main signal by a predetermined ratio; the upper limit of the amplitude of the superimposed signal is a value obtained by adding the amplitude of the main signal to a value obtained by multiplying the amplitude of the main signal by the predetermined ratio, a lower limit value of the amplitude of the superimposed signal is a value obtained by subtracting a value obtained by multiplying the amplitude of the main signal by the predetermined ratio from the amplitude of the main signal; The optical transmitter unit an optical signal output unit that outputs the main signal; an optical signal amplifier that amplifies the main signal output by the optical signal output unit to superimpose the superimposed signal on the main signal; a driver that drives the optical signal output unit and the optical signal amplifier unit, the control unit stores in advance information linking the temperature of the optical transceiver with a command to be given to the drive unit; the control unit refers to the information in accordance with the temperature measured by the temperature sensor and issues a command to the drive unit; the driver controls the optical signal amplifier in response to the given command so that the average value of the intensity of the optical signal output from the optical signal amplifier is maintained constant, and so that the main signal is modulated by amplitude shift keying into a signal having a waveform whose amplitude transitions between two levels, and so that the superimposed signal is superimposed. Optical communication system.

12. Two opposing optical transmission devices each having a plurality of optical transceivers and a first optical multiplexer / demultiplexer that multiplexes and outputs optical signals output by the plurality of optical transceivers and demultiplexes received optical signals to the plurality of optical transceivers according to channels; an optical cable connecting the two opposing optical transmission devices, The optical transceiver of one of the optical transmission devices includes: an optical transmitter that superimposes an optical signal for issuing a command to another optical transceiver of another optical transmission device on a main signal that is an optical signal for transmitting communication data to the other optical transceiver, and outputs the superimposed optical signal; an optical receiving unit that receives an optical signal from the other optical transceiver; a control unit that controls the optical transmitting unit and the optical receiving unit, The optical transmitter unit the superimposed signal, which is the optical signal superimposed on the main signal, is superimposed on the main signal by modulating the main signal into a signal having a waveform whose amplitude transitions between two levels using amplitude shift keying; controlling the amplitude of the superimposed signal based on a value obtained by multiplying the amplitude of the main signal by a predetermined ratio; the upper limit of the amplitude of the superimposed signal is a value obtained by adding the amplitude of the main signal to a value obtained by multiplying the amplitude of the main signal by the predetermined ratio, a lower limit value of the amplitude of the superimposed signal is a value obtained by subtracting a value obtained by multiplying the amplitude of the main signal by the predetermined ratio from the amplitude of the main signal; The optical transmitter unit an optical signal output unit that outputs the main signal; an optical signal amplifier that amplifies the main signal output by the optical signal output unit to superimpose the superimposed signal on the main signal; a driver that drives the optical signal output unit and the optical signal amplifier unit, the control unit stores in advance information linking an elapsed time since the start of operation of the optical transceiver with a command to be given to the drive unit; the control unit refers to the information in accordance with the elapsed time and issues a command to the drive unit; the driver controls the optical signal amplifier in response to the given command so that the average value of the intensity of the optical signal output from the optical signal amplifier is maintained constant, and so that the main signal is modulated by amplitude shift keying into a signal having a waveform whose amplitude transitions between two levels, and so that the superimposed signal is superimposed. Optical communication system.

13. Two opposing optical transmission devices each having a plurality of optical transceivers and a first optical multiplexer / demultiplexer that multiplexes and outputs optical signals output by the plurality of optical transceivers and demultiplexes received optical signals to the plurality of optical transceivers according to channels; an optical cable connecting the two opposing optical transmission devices, The optical transceiver of one of the optical transmission devices includes: an optical transmitter that superimposes an optical signal for issuing a command to another optical transceiver of another optical transmission device onto a first main signal that is an optical signal for transmitting communication data to the other optical transceiver, and outputs the superimposed optical signal as a first optical signal; an optical receiving unit that receives a second optical signal from the other optical transceiver; a control unit that controls the optical transmitting unit and the optical receiving unit, The optical transmitter unit a first superimposed signal, which is the optical signal superimposed on the first main signal, is superimposed on the first main signal by modulating the first main signal by amplitude shift keying to a signal having a waveform whose amplitude transitions between two levels; controlling the amplitude of the first superimposed signal based on a value obtained by multiplying the amplitude of the first main signal by a predetermined ratio; the second optical signal is an optical signal on which a second superimposition signal, which is an optical signal for issuing a command to the optical transceiver, is superimposed, the second optical signal being obtained by modulating a second main signal, which is an optical signal corresponding to communication data, into a signal having a waveform in which the amplitude transitions between two levels by amplitude shift keying using Manchester coding; The optical receiving unit refers to synchronization information included in the second superimposed signal, After starting to detect a transition in the level of the second superimposed signal, the level of the second superimposed signal is detected at a timing corresponding to each period of Manchester encoding in the synchronization information; When there is a timing at which the level of the second superimposed signal does not change during the detection of the level at the timing of each period, the timing at which the transition of the level of the second superimposed signal is detected is delayed by 1 / 2 of the period; When there is no timing at which the level of the second superimposed signal does not change during the detection of the level at the timing for each period, the timing for detecting the transition of the level of the second superimposed signal is maintained; detecting a level transition of the second superimposed signal at the determined timing; Optical communication system.

14. An optical transceiver comprising: an optical transmitter that outputs an optical signal for issuing a command to another optical transceiver, superimposed on a main signal that is an optical signal for transmitting communication data to the other optical transceiver; an optical receiver that receives the optical signal from the other optical transceiver; a control unit that controls the optical transmitter and the optical receiver; and a temperature sensor that measures the temperature of the optical transceiver, the superimposed signal, which is the optical signal superimposed on the main signal, is superimposed on the main signal by modulating the main signal into a signal having a waveform whose amplitude transitions between two levels using amplitude shift keying; controlling the amplitude of the superimposed signal based on a value obtained by multiplying the amplitude of the main signal by a predetermined ratio; the upper limit of the amplitude of the superimposed signal is a value obtained by adding the amplitude of the main signal to a value obtained by multiplying the amplitude of the main signal by the predetermined ratio, a lower limit value of the amplitude of the superimposed signal is a value obtained by subtracting a value obtained by multiplying the amplitude of the main signal by the predetermined ratio from the amplitude of the main signal; The optical transmitter unit an optical signal output unit that outputs the main signal; an optical signal amplifier that amplifies the main signal output by the optical signal output unit to superimpose the superimposed signal on the main signal; a driver that drives the optical signal output unit and the optical signal amplifier unit, the control unit stores in advance information linking the temperature of the optical transceiver with a command to be given to the drive unit; the control unit refers to the information in accordance with the temperature measured by the temperature sensor and issues a command to the drive unit; the driver controls the optical signal amplifier in response to the given command so that the average value of the intensity of the optical signal output from the optical signal amplifier is maintained constant, and so that the main signal is modulated by amplitude shift keying into a signal having a waveform whose amplitude transitions between two levels, and so that the superimposed signal is superimposed. A method for controlling an optical transceiver.

15. An optical transceiver comprising: an optical transmitter that outputs an optical signal for issuing a command to another optical transceiver by superimposing the optical signal on a main signal, which is an optical signal for transmitting communication data to the other optical transceiver; an optical receiver that receives the optical signal from the other optical transceiver; and a control unit that controls the optical transmitter and the optical receiver, the superimposed signal, which is the optical signal superimposed on the main signal, is superimposed on the main signal by modulating the main signal into a signal having a waveform whose amplitude transitions between two levels using amplitude shift keying; controlling the amplitude of the superimposed signal based on a value obtained by multiplying the amplitude of the main signal by a predetermined ratio; the upper limit of the amplitude of the superimposed signal is a value obtained by adding the amplitude of the main signal to a value obtained by multiplying the amplitude of the main signal by the predetermined ratio, a lower limit value of the amplitude of the superimposed signal is a value obtained by subtracting a value obtained by multiplying the amplitude of the main signal by the predetermined ratio from the amplitude of the main signal; The optical transmitter unit an optical signal output unit that outputs the main signal; an optical signal amplifier that amplifies the main signal output by the optical signal output unit to superimpose the superimposed signal on the main signal; a driver that drives the optical signal output unit and the optical signal amplifier unit, the control unit stores in advance second information that associates an elapsed time since the start of operation of the optical transceiver with a command to be given to the drive unit; the control unit refers to the second information in accordance with the elapsed time and issues a second command to the drive unit; the driver controls the optical signal amplifier in response to the second command given thereto so that an average value of intensity of the optical signal output from the optical signal amplifier is maintained constant, and so that the main signal is modulated by amplitude shift keying into a signal having a waveform whose amplitude transitions between two levels, and so that the superimposed signal is superimposed. A method for controlling an optical transceiver.

16. An optical transceiver comprising: an optical transmitting unit that superimposes an optical signal for issuing a command to another optical transceiver on a first main signal that is an optical signal for transmitting communication data to the other optical transceiver and outputs the superimposed optical signal as a first optical signal; an optical receiving unit that receives a second optical signal from the other optical transceiver; and a control unit that controls the optical transmitting unit and the optical receiving unit, a first superimposed signal, which is the optical signal superimposed on the first main signal, is superimposed on the first main signal by modulating the first main signal by amplitude shift keying to a signal having a waveform whose amplitude transitions between two levels; controlling the amplitude of the first superimposed signal based on a value obtained by multiplying the amplitude of the first main signal by a predetermined ratio; the second optical signal is an optical signal on which a second superimposition signal, which is an optical signal for issuing a command to the optical transceiver, is superimposed, the second optical signal being obtained by modulating a second main signal, which is an optical signal corresponding to communication data, into a signal having a waveform whose amplitude transitions between two levels by amplitude shift keying using Manchester coding; The optical receiving unit refers to synchronization information included in the second superimposed signal, After starting to detect a transition in the level of the second superimposed signal, the level of the second superimposed signal is detected at a timing corresponding to each period of Manchester encoding in the synchronization information; When there is a timing at which the level of the second superimposed signal does not change during the detection of the level at the timing of each period, the timing at which the transition of the level of the second superimposed signal is detected is delayed by 1 / 2 of the period; When there is no timing at which the level of the second superimposed signal does not change during the detection of the level at the timing for each period, the timing for detecting the transition of the level of the second superimposed signal is maintained; detecting a level transition of the second superimposed signal at the determined timing; A method for controlling an optical transceiver.

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